Expression of neuronal nicotinic acetylcholine receptor subunit genes in the rat autonomic nervous system

In the autonomic nervous system efferent signals are relayed in sympathetic and parasympathetic ganglia. Fast synaptic transmission between pre- and postsynaptic neurons is achieved by neuronal nicotinic acetylcholine receptors (nAChRs). There is still little known about the subunit composition of these receptors. Establishing the subunit composition of native neuronal nAChRs is important for the understanding of their functional properties both in vivo and after expression in heterologous expression systems. We have combined in situ hybridization and autoradiography to detect the presence of mRNAs encoding subunits of neuronal nAChRs in sympathetic and parasympathetic ganglia. Inspection of the autoradiographs showed that the hybridization signal of five riboprobes (alpha 3, alpha 4-1, alpha 7, beta 2 and beta 4) was significantly higher than the unspecific signal obtained with sense riboprobes. The distribution of alpha 7 was tissue-dependent: alpha 7 riboprobe binding was detected in the neurons of the superior cervical ganglion, adrenal medulla and ciliary ganglion. In contrast, the alpha 7 hybridization signal was found only in a small fraction (1-3%) of the neurons of the sphenopalatine and otic ganglia. Our results are consistent with the idea that alpha 3 mRNA expression levels are somewhat higher than those of alpha 7, alpha 4-1, beta 2 and beta 4.